1. Field of the Invention
The invention relates to a freewheel clutch having first and second clutch parts, a detent pawl supported with freedom of movement on one of the clutch parts, a recess in the other of the clutch part to accept the detent pawl, and a control element for moving the pawl out of the recess and into a position remote from the recess.
2. Description of the Related Art
Freewheel clutches are used, for example, in the hubs of the running wheels of bicycles and are usually used to produce or to release a form-locking connection between the clutch parts as a function of the rotational direction of a driving clutch part relative to a driven clutch part.
A freewheel clutch of this type is described in, for example, EP 0 787 922 A2. This freewheel clutch has a radially inner clutch part and a radially outer clutch part which encloses the radially inner clutch part. Several pawls are arranged on the radially inner clutch part which are pretensioned in a radially outward direction by spring elements. A ring of recesses is provided in the radially outer clutch part. The pawls can be urged out of the recesses in the radially inward direction by a control mechanism with a driver which can be moved against the pawl. This design of the control mechanism has the advantage that the pawls are out of the recesses when the clutch parts are rotating in the direction in which no positive, form-locking connection is to be produced between them. This arrangement avoids the generation of unpleasant noise and minimizes the wear on the recesses and the pawls. A problem with this known freewheel clutch, however, is that the spring elements are difficult to install and to hold in place. In addition, very large forces are required to move the pawls against the force of the spring elements. Accordingly, only a few pawls are typically used in this design. The pawls and the recesses must therefore be very strong and are accordingly made of steel.
Another freewheel clutch in which the control element can be moved by frictional forces between a position in which the pawls are inside the recesses and a position in which the pawls are outside of the recesses is known from DE AS 1,575,963. In this device, all of the pawls are pretensioned by a single spring in the radially outward direction into the recesses. The problem with this device is that it is difficult to install the spring element and that high forces are required to move the pawls against the force of the spring.
It is an object of the present invention to design a freewheel clutch for a bicycle hub having first and second clutch parts, a detent pawl supported with freedom of movement on one of the clutch parts, a recess in the other of the clutch part to accept the detent pawl, and a control element for moving the pawl out of the recess and into a position remote from the recess such that it is very easy to install and that very small forces are sufficient to move the pawls.
The object of the present invention is met by a freewheel clutch having a second control element provided for moving the pawls into the recesses.
The use of the second control element in the present invention obviates the requirement for a spring element to move the pawls. Accordingly, there is no need for complicated holders and guides for the spring elements. The freewheel clutch according to the invention may thus be installed very easily and may also be produced at low cost. The elimination of the spring element allows the pawls to be moved by forces which are much smaller than those required in the known freewheel clutch. Furthermore, the present invention allows a large number of pawls to be used because only a small amount of force is required to move the pawls. When a positive, form-locking connection is present between the clutch parts, the forces which develop are therefore distributed over the large number of pawls and the walls of the recesses. In the most favorable case, the pawls and the recesses may be made of a light-weight material with a strength much less than that of steel such as aluminum or magnesium or their alloys.
In accordance with a further embodiment of the present invention, the pawls may be actuated by a simple design in that at least one of the control elements is connected to an auxiliary pawl element such that the auxiliary pawl element latches itself into a recess when the clutch parts rotate relative to each other in an intended direction.
The freewheel clutch according to the present invention may be operated quietly when at least one of the control elements is connected to an auxiliary friction element arranged to produce a friction-locking connection between the clutch parts. Since the present invention requires only a small amount of force to move the pawls, the design of the freewheel clutch according to the present invention requires very small frictional forces.
A further problem of the known freewheel clutch is that there are a very large number of individual components which makes assembly of the clutch difficult. Accordingly, it is very expensive to fabricate the known freewheel clutch. Fabrication of the freewheel clutch according to the present invention is simplified when the control elements and the auxiliary pawl element or the auxiliary friction element are mounted on an actuating ring, which is movable with respect to the clutch parts. In the simplest case, the components may simply be inserted into each other during the assembly process. Another advantage of this design is that the actuating ring and the pawls may be put together to form a preassembled unit, which is easily assembled with the first and second clutch parts during final assembly.
In a further embodiment of the present invention, the pawls are controlled by a design in which the auxiliary pawl element is held under pretension in the recess. Because only small forces are required to move the pawls, a large number of pawls can be moved by only one or two auxiliary pawl elements. As a result, unpleasant noise is minimized.
Noise during the movement of the clutch parts relative to each other may be further minimized according to a further embodiment in which the auxiliary friction element is held under pretension against the clutch part with the recesses.
In yet another embodiment, the auxiliary pawl element or the auxiliary friction element can be held reliably in its intended position by mounting the auxiliary pawl element or the auxiliary friction element on a spring element which projects from the actuating ring. This design also contributes to a further simplification of the process of assembling the freewheel clutch according to the present invention.
The spring element may be installed at a slight angle relative to a tangent to the clutch part with the recesses. As a result, the auxiliary pawl element or the auxiliary friction element transmits small forces in one of the relative directions of rotation of the clutch parts and transmits very large forces in the opposite direction of relative rotation. This ensures that, after the form-locking connection between the clutch parts has been released, the detent pawls will be able to move reliably and that only a small amount of friction energy will be produced.
The freewheel clutch according to the invention may be made compact by providing the recesses in the radially inner part of the clutch.
In yet a further embodiment of the present invention, known freewheel clutches may be converted with little mechanical effort to freewheel clutches according to the present invention when the recesses are in the radially outer clutch part.
The freewheel clutch according to the present invention can be designed easily as an axial freewheel when the pawl is allowed to move in the axial direction and when the recesses and the detent pawl face each other in the axial direction.
The freewheel clutch designed as a radial freewheel requires very small dimensions in the radial direction when the actuating ring is located axially next to the area of the clutch parts with the recesses and pawl and when the control elements project into the area of the clutch parts with the recesses and the pawl.
To further reduce the number of components of the freewheel clutch according to the present invention, the auxiliary pawl element may be designed as an integral part of the spring element which projects from the actuating ring.
The control elements may, for example, work together with the associated pawl via knee levers. Alternatively, the control elements and the pawl may be designed very simply and fabricated very easily by providing the pawl with two guide bevels for the control elements.
To achieve a further reduction in the number parts to be manufactured, it is helpful in accordance with another embodiment of the present invention to design the control elements as a common component which is moveable in a guide groove of the pawl.